Method of making vanadium oxide-potassium oxide catalysts of selected porosity



United States Patent C) 4 Claims. (a. 252456) This invention relates to the manufacture of S by the catalytic oxidation of S0 on vanadium-potassiumsilica catalysts. The invention also relates to the manufacture of novel catalysts for this process. The invention also includes a novel method for producing the new catalysts,

In the manufacture of S0 by the catalytic oxidation of S0 it is customary to mount the active catalyst which is composed of vanadium oxide and potassium oxide, on a silica support. During the preparation of the granules of the catalyst an effort is made to produce the largest catalytic surface possible. At the ame time, it is known that when one is dealing with catalytic activity the whole answer to the problem is not found in mere surface area. It is known that in gaseous catalytic reactions, such as the one involved in this invention, the kinetic diffusional coetlicients of the gas must also be considered as well as the geometric conformation of the granules.

In the catalytic production of S0 the process proceeds first at high temperature, usually between 440 and 550 C., and then the temperature of the reaction falls as the reaction proceeds until it finally is below 400 C. It is also known by this inventor that the efiiciency of these catalyst is not the same at different temperatures. For instance, the catalytic oxidation of S0,; to S0 goes to substantial completion only at relatively low temperature, which constitutes an imperfection in the process because of relatively low rate of reaction at such temperatures. For example, when a gas containing 7% of S0 11% of O and 82% of N is sent into contact with a vanadium-silica catalyst the conversion at 440 C. is only 98%, whereas at 400 C. the conversion reaches the rate of 99.2%.

It is an object of this invention to produce a catalyst which will have high efiiciency at high temperature and other catalysts which will have high efficiency at lower temperature and by the selective use of these novel catalysts to improve the overall efiiciency of the catalytic conversion.

These objects of the invention have been accomplished by a method of oxidizing S0 gas to S0 gas on a vanadium, potassium, silica catalyst which comprises commencing the reaction on a said catalyst having a majority of pores above about 3000 A. radius at a temperature between about 440 and 550 C., and at a temperature below 440 continuing the reaction on a similar catalyst having a majority of pores of materially smaller radius.

The novel catalysts which are used in the novel process are a porous silica-vanadium oxide-potassium oxide catalyst having at least 60% of pores of radius in the range of about 1000 and 3000 A., and a porous silica-vanadium oxide-potassium oxide catalyst having at least 60% of pores of radius in the range between about 50 and 500 A.

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The novel method of preparing a catalyst comprises depositing vanadium oxide and potassium oxide on finely divided silica, drying the mass, crumbling the mass and screening it, compressing the graded particles, thereby producing granules of about 6 mm. diameter, and calcining and cooling the mass.

In order to prepare the novel catalyst for use in the novel process it was necessary to invent a method of preparing the catalysts by which pores sizes could be controlled and this will be described in detail hereinafter.

By virtue of these new catalysts We can produce high speeds of reaction at temperatures below 400 C. and these can be used during the latter stages of the catalytic oxidation when the temperature of the reaction mixture has been appreciably reduced. On the other hand, at the beginning of the catalytic oxidation we have provided catalysts having excellent activity in the temperature zone between 440 and 550 C. Thus, by beginning the catalytic oxidation on the catalyst of high efiiciency at high temperature and thereafter continuing the reaction on the catalyst of high efiiciency at the lower temperature a material improvement in the overall efficiency of the process is obtained.

I have established that the efficiency of the catalyst is a function of the radius of the pores of the catalyst and that the process proceeds best at high temperature with catalysts having larger pores and at low temperature with catalysts having pores of smaller radius.

The catalysts employed consist essentially of K 0 which is present in 3 to 20% of the weight of the catalyst, and preferably from 9 to 11%, V 0 which is present from 3 to 15%, and preferably from 7 to 9%, the balance to make about being SiO I have shown that these catalysts, when used at temperatures not substantially higher than 400 C. for the oxidation of S0 to S0 should have the highest possible content of pores having a radius between 50 and 500 A., that those used between 400 and 440, approximately, should have the highest possible content of pores of the radius of 1000 to 3000 A., and that those used at temperatures above about 440 C. should have as high a content as possible of pores on the order of 5000 A. radius.

There are a number of procedural steps that one may adopt to produce pores of the desired size. One of these is the choice of the granulometry of the support. If one seeks to produce catalysts having pores of 50 to 500 A. radius one may use powdered silica of which the individual particles have diameters on the order of some tens to some hundreds of A.

To produce pores having a radius of about 1000 to 3000 A. one may use a powdery silica prepared by the precipitation from a silicate. For instance by the method of French Patent No. 1,001,884, or a silica as is prepared in French Patents No. 795,594 and No. 836,782. It is equally possible to use a natural silica which has been micronized.

In forming the catalyts one may satisfactorily deposit the catalytic metal oxides on the silica, dry the catalyst, and break it up in particles of convenient size, for instance sizes capable of passing a number 31 afnor screen. The product is then agglomerated under the pressure stated above into granules of about 6 mm. diameter and calcined.

In producing the pores of selected size one may also use the temperature of calcination with effect to produce a catalyst having a silica support of 50 to 500 A. A calcination carried out at 400 to 500 C. tends to produce fine porosity with radii inferior to about 500 A. When the temperature of calcination is carried to 700 to 800 C. the pores will have radii on the order of 2000 to 3000 A.

Another element which influences the porosity is the addition to the support, during the deposition of the active catalyst of a micronized combustible or volatile product such as micronized sulfur or micronized carbon black. When these products vaporize during the calcination, pores corresponding to the size of the particles are established in the silica support.

Yet another element which acts upon the porosity is the simutaneous use of silicas of different granular size. By mixing silica in particles of a few 1000 A. in diameter with a minor percentage of silica in particles of several hundreds of A. the fineness of the pores formed between the particles in the catalytic mass is increased.

The following examples are for the purpose of illustration and do not constitute a limitation on the generality of what is elsewhere herein stated and claimed.

Example 1 A solution is prepared containing 185 grams of potassium hydroxide, containing 28% K 0, and 49 grams of 85% commercial V This mixture is treated with 215 grams of 16 sulfuric acid with vigorous agitation. 19 grams of NH OH are added and the mixture thus obtained is slowly poured onto 400 grams of finely divided silica (in this case levilite) in a mixer. The mixture of finely divided components is continued and a small amount of water may be added. After about a half hour the paste is removed from the mixer, dried at not above 100 C., and fragmented to pass a 31 afnor screen. The product is agglomerated by compression at 1000 l g./cm. in granules of 6 mm. in diameter and is calcined at 600 C. The catalytic granules thus prepared have a total porosity of 1 cm. /g., of which 80% are due to pores having a radius between 1000 and 3000 A.

The addition of 10% by weight of sulfur to the silica may be adopted to improve the porosity if desired.

The catalyst thus prepared may be subjected to catalytic tests for the transformation of S0 to S0 In one of these tests a gas containing 7% S0 11% O and 82% N was passed into contact with the catalyst at a space velocity of 1900 h.- under isothermal conditions, producing the following rates of conversion: 18.5% at 390 C., 28% at 400 C., and 56% at 425 C.

Example 2 A mixture like that of Example 1 was prepared and poured slowly upon 400 grams of powdered silica having grain dimensions on the order of 150 A. The mixture is mixed and the product dried, broken up, agglomerated under pressure, as aforesaid, and calcined at about 600 C. The catalyst have a total porosity of .65 cm. /g., of which 80 is due to pores of a radius between and 500 A.

When used to catalyze the same gases of Example 1 the rate of conversion was 22% at 390 C., 30.5% at 400 C., and 50% at 420 C.

In another test the calcination temperature was 750 C. and the catalyst produced had a conversion rate of 15.5% at 390 C., 54.5% at 420 C. 80% of the porosity was due to pores of a radius between 1000 and 3000 A.

Example 3 Nautral kieselguhr finely divided, was mixed with 10% of carbon black of particle size on the order of 100 A.

and the mixture was subjected to the treatments specified were due to pores having a radius between 1000 and 3000 A. During the catalytic operation recited in Example 1 rates of conversion of these catalysts were 13% at 390 C., 23% at 400 C., and 54% at 430 C.

Example 4 Example 2 wa carried out identically with the exception that silica gel suitably prepared was used in place of the other form of silica. The results under tests proved to be equally satisfactory.

The carbon black is preferred, particularly for use with levilite or powdered silica.

Example 5 A solution is prepared containing 185 grams of potassium hydroxide, containing 28% K 0 and 49 grams of commercial V 0 This mixture is treated with 215 grams of 16 sulfuric acid with vigorous agitation. 19 grams of NH OH are added and the mixture thus obtained is slowly poured on 400 grams of finely divided kiselguhr in a mixer as in Example 1. The finely divided product is agglomerated by extrusion in granules of 6 mm. in diameter and is calcined at 600 C. The catalytic granules thus prepared have a total porosity of 1 cm. /g., of which 70% are due to pores having a radius between 3000 and 5000 A.

The catalyst thus prepared may be subjected to catalytic tests for the transformation of S0 to S0 In one of these tests a gas containing 7% S0 11% O and 82% N was passed into contact with the catalyst at a space velocity of 1900 h.- under iso-thermal conditions, producing the following rates of conversion: 11.2% at 390 C., 22.6% at 400 C., and 58% at 460 C.

The advantages of the invention include the prepara- ,tion of superior silica-vanadium-potassium catalysts, the improven1ent of the process of catalytically oxidizing S0 and a process for producing silica-base catalysts having a major proportion of pores of a selected size.

By comparing the small-pore catalyst of Example 2 with the large-pore catalyst of Example 2 it will be found that the conversion rate of the former is better than the conversion rate of the latter at low temperature, which fits the small-pore catalyst for use in the last stages of the process. On the other hand the large-pore catalyst gives a better conversion at high temperature than the small-pore catalyst and is better adapted for use in the early high temperature phase of the reaction.

As many apparently widely different embodiments of the present invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments.

What is claimed is:

1. A method of making vanadium oxide-potassium oxide-silica catalysts having 3 to 20% K 0, 3 to 15% V 0 and the balance being SiO having pores a majority of which are in the range of radii of 50 to 500 A. which comprises mixing aqueous KOH with V 0 and dilute sulphuric acid in such quantity that the KOH is not wholly neutralized, mixing the sulphated reaction product with NH OH and the product with silica particles having diameters on the order of several tens to several hundreds of A., drying the mass at not substantially over C., and calcining the dried product circa 400-500 C.

2. A method of making vanadium oxide-potassium oxide-silica catalysts having 3 to 20% K 0, 3 to 15% V 0 and the balance being Si0 having a majority of pores of radius in the range from about 1000-3000 A. which comprises mixing aqueous KOH with V 0 and dilute sulfuric acid in such quantity that the KOH is not wholly neutralized, mixing the sulphated reaction product with NH OH and the product with silica particles having fineness equivalent to that prepared by precipitation from a silicate, drying the mass at not substantially over 100 C., and calcining the dried product circa 500-800 C.

3. A method of making vanadium oxide-potassium oxide-silica catalysts having 3 to 20% K 0, 3 to 15% V 0 and the balance being SiO with pores of selected sizes in the range of about 50 to 3000 A. which comprises mixing aqueous KOH with V 0 and dilute sulfuric acid in such quantity that the KOH is not wholly neutralized, mixing the sulfated reaction product with NH OH and the product with micronized silicous material a major part of which is not substantially over 5000 A. in diameter, drying the product at not substantially over 100 C. and calcining the dried product circa 400-800 C.

4. The process of claim 3 in which the dried mass is agglomerated in granules before the calcination.

References Cited by the Examiner UNITED STATES PATENTS 1,887,978 11/32 Joseph 252-456 1,893,812 1/33 Weil 252-456 6 10/35 Cummings 252-456 2/36 Joseph 23-456 4/47 Rosenblatt et al. 23-175 4/59 Strang 23-175 4/ 54 Darby 252-456 10/57 Dixon et a1 252-456 2/ 61 Chromitz et a1 252-456 X 9/61 Reitmeier 252-455 6/62 Nerets et al. 260-3464 10/ 63 Royer et al. 252-456 X FOREIGN PATENTS 5/50 Great Britain.

MAURICE A. BRINDISI, Primary Examiner. 

1. A METHOD OF MAKING VANADIUM OXIDE-POTASSIUM OXIDE-SILICA CATALYSTS HAVING 3 TO 20% K2O, 3 TO 15% V2O5, AND THE BALANCE BEING SIO2 HAVING PORES A MAJORITY OF WHICH ARE IN THE RANGE OF RADII OF 50 TO 500 A. WHICH COMPRISES MIXING AQUEOUS KOH WITH V2O5 AND DILUTE SULPHURIC ACID IN SUCH QUANTITY THAT THE KOH IS NOT WHOLLY NEUTRALIZED, MIXING THE SULPHATED REACTION PRODUCT WITH NH4OH AND THE PRODUCT WITH SILICA PARTICLES HAVING DIAMETERS ON THE OUTER OF SEVERAL TENS TO SEVERAL HUNDREDS OF A., DRYING THE MASS AT NOT SUBSTANTIALLY OVER 100*C., AND CALCINING THE DRIED PRODUCT CIRCA 400-500*C. 